Local Anesthetics (8-25-15)

Question 1

Cocaine

Answer 1

• Indication: topical use mainly for minor surgeries (nasopharynx, etc)
• Ester or amide: Ester, equally as potent as mepivacaine (#2 potency overall)
• MOA: block Na channels on neurons; vasoconstriction
• Drug action: bind & block OPEN or inactivated Na channels; prevent re-uptake of NE at adrenergic terminals
• Onset: FAST
• Duration: medium (1 hr)
• Toxicity/side-effects: PABA Allergy, CNS toxicity

*Note: TOPICAL USE, INTRINSIC VASOCONSTRICTOR

Question 2

Procaine

Answer 2

(NOVOCAIN)

• Indication: infiltration, nerve block, spinal anesthesia
• Ester or amide: Ester, MOST POTENT OVERALL (#1), all potency comparisons are to procaine
• MOA: block Na channels on neurons
• Drug action: bind & block OPEN or inactivated Na channels
• Onset: SLOW
• Duration: short (30-45 min)
• Toxicity/side-effects: PABA Allergy, CNS toxicity

*Note: Use EPI to keep local

Question 3

Tetracaine

Answer 3

• Indication: Spinal anesthesia; less potent than procaine
• Ester or amide: Ester
• MOA: block Na channels on neurons
• Drug action: bind & block OPEN or inactivated Na channels
• Onset: SLOW
• Duration: long (2-5 hours)
• Toxicity/side-effects: PABA Allergy, CNS toxicity

Question 4

Benzocaine

Answer 4

• Indication: topical pain relief, usually as an OTC spray
• Ester or amide: Ester
• MOA: block Na channels on neurons
• Drug action: bind & block OPEN or inactivated Na channels
• Onset: n/a, topical use only
• Duration: n/a, topical use only
• Toxicity/side-effects: PABA Allergy, CNS toxicity

*Note: TOPICAL USE only!

Question 5

Lidocaine

Answer 5

• Indication: epidural/subarachnoid, infiltration, nerve block
• Ester or amide: amide (two I’s), third most potent after mepivacaine, cocaine and of course, procaine
• MOA: block Na channels on neurons
• Drug action: bind & block OPEN or inactivated Na channels
• Onset: FAST
• Duration: medium
• Toxicity/side-effects: CNS as usual, pretty much non-allergic, have liver metabolism

*Note: in neuraxial blocks, nerves at or below the level of the injection site are blocked!

Question 6

Mepivacaine

Answer 6

• Indication: epidural, infiltration, nerve block
• Ester or amide: Amide (two I’s), equally as potent as cocaine (#2 potency overall)
• MOA: block Na channels on neurons
• Drug action: bind & block OPEN or inactivated Na channels
• Onset: FAST
• Duration: medium
• Toxicity/side-effects: CNS as usual, pretty much non-allergic, have liver metabolism

*Note: Respiratory arrest in high spinal blocks is NOT due to phrenic nerve! It is from hypoperfusion of respiratory center in medulla.

Question 7

Bupivacaine

Answer 7

• Indication: epidural/subarachnoid, infiltration, nerve block
• Ester or amide: Amide (two I’s)
• MOA: block Na channels on neurons
• Drug action: bind & block OPEN or inactivated Na channels
• Onset: SLOW
• Duration: long
• Toxicity/side-effects: CNS as usual, MORE CARDIOTOXIC than others in this group!!

*Note: post-dural puncture headaches (#2 side effect in neuraxial block) are more likely in young, pregnant, females

Question 8

Ropivacaine

Answer 8

• Indication: epidural
• Ester or amide: Amide (two I’s)
• MOA: block Na channels on neurons
• Drug action: bind & block OPEN or inactivated Na channels
• Onset: SLOW
• Duration: long
• Toxicity/side-effects: CNS as usual, pretty much non-allergic, have liver metabolism

*Note: neuraxial block is contraindicated in bowel obstruction b/c of increased motility